1. Field of the Invention
The present invention relates to a method for the preparation of ceramic cores intended to be used for the precision casting of parts produced by means of lost-wax casting processes.
2. Summary of the Prior Art
The application of such casting processes of which the general technical knowledge is well dissemeninated within the foundry art is intended primarily for the production of high precision parts and is especially suited to the manufacture of aeronautical parts.
One example of such applications is the provision within turbine blades of very complex internal cooling arrangements. The manufacture of such parts by foundry procedures using the lost-wax process requires the use of ceramic cores which in order to reproduce these cooling arrangements, have inevitably multiple cavities, thin walls and complex shapes. As a result these cores are very fragile and it follows that multiple handling or the application of stresses risk causing damage by rupture or carcking.
The formation of wax models enrobing cores of this type in the processes of the lost-wax type thus encounter difficulties in practical application which are not wholly resolved satisfactorily by the operational procedures hitherto applied. In practice, the fragility of the cores hinders the injection of the wax, during the enrobing operation of the cores by the modelling wax, to a pressure sufficient to enable compensation for volumetric shrinkage of the wax in the larger volumes where local thicknesses are much greater. Now these shrinkages cause defects in the shape which show up in the parts to be made in a nonacceptable manner and furthermore it is not always possible to apply correcting measures in a repetitive manner in such a way as to correct such defects.
One solution to this problem, which the practitioners of the technical art concerned have tentatively sought to apply. consists in filling manually with liquid wax all the cavities of the ceramic cores before the enrobing operation. But this manual operation apart from inconveniences of practical application taking into account the costs, the prolongation of the manufacturing cycles, gives rise to numerous handling operations increasing the risks of damage resulting from the fragility of the cores and gives rise to the necessity of effecting numerous retouching operations, while at the same time essentially relying upon the dexterity of an operator.
An object of the present invention is to provide a method for the preparation of ceramic cores which resolves the problems hereinafter discussed.